MALA-SPRAY

Malathion (chemathion, mala-spray) requires conversion to malaoxon (replacement of a sulfur atom with oxygen in vivo, conferring resistance to mammalian species). Malathion can be detoxified by hydrolysis of the carboxyl ester linkage by plasma carboxylesterases, and plasma car-boxylesterase activity dictates species resistance to malathion. The detoxification reaction is much more rapid in mammals and birds than in insects. Malathion has been employed in aerial spraying of relatively populous areas for control of Mediterranean fruit flies and mosquitoes that harbor and transmit viruses harmful to human beings (e.g.. West Nile encephalitis virus). Evidence of acute toxicity from malathion arises only with suicide attempts or deliberate poisoning. 

Some published data are difficult to interpret. For example, 26 men were exposed in tanks and holds of two merchant vessels being painted (solvents) and sprayed with mala-thion 20% and pyrethrin 1.5%, with piperonyl butoxide in toluene. They showed losses of concentration, unawareness of danger and unconsciousness at toluene levels estimated as 10,000 to 12,000 ppm and up to 30,000 ppm below waist level. Additive effects of the neurotoxic insecticides were not discussed. 

---